Thirteen months is when the nap transition question moves from theoretical to practical. Your toddler may be consistently fighting one nap, and unlike at 12 months (which was likely the regression), at 13 months some babies genuinely are starting to show readiness for one nap. But "showing readiness" and "being ready" are two different things.
The 2-to-1 nap transition is the hardest nap transition your child will go through. It requires them to stay awake for much longer stretches (5+ hours instead of 3 to 4), and their body needs time to adjust. Rushing it leads to overtiredness, which creates a cascade of worse naps, more night wakings, and earlier mornings.
If you're uncertain, stay with 2 naps. The cost of keeping 2 naps a little too long is minimal (maybe a slightly later bedtime). The cost of dropping to 1 nap too early is significant (overtired toddler, worse sleep across the board). When in doubt, wait.